When light is irradiated to certain metal microstructures such as metal nanoparticles, the free electrons inside metal resonates with the incident light and causes a collective oscillation, thereby expressing an enhanced electromagnetic field. This phenomenon is known as a Localized Surface Plasmon Resonance (LSPR). This LSPR is especially enhanced in a gap of metal nanoparticle aggregates and the like, and when a molecule absorbs to the gap, the Raman scattering cross-section area of the absorbed molecule is enhanced 10 to the 10th power to 10 to the 14th power compared to the ordinary Raman scattering cross-section area, and a remarkably strong Raman scattering is detected. This approach is called Surface Enhanced Raman Scattering (SERS).
A Raman spectroscopic analysis is a spectroscopic technique used such as in molecular identification of an analyte practiced based on a Raman scattered light generated by irradiating excitation light to the analyte. Since the Raman scattered light is extremely weak, it has an issue that detection is difficult. Accordingly, methods for generating a Raman scattered light with high intensity by using the aforementioned phenomenon called Surface Enhanced Raman Scattering are proposed. The effect of the Raman scattered light being enhanced by SERS (hereinafter called the “SERS effect”) is high when the size of the space of the metal particles in-between is of approximately tens of nm or less in size. To obtain such high SERS effect, methods for forming fine spaces in-between the metal particles are variously proposed as shown below.
The substrate for surface enhanced Raman scattering spectroscopy described in nonpatent literature 1 has an inverted pyramidal pit of micron order formed with its inside coated with gold. The SERS effect is produced by granulated gold being adjacent in the bottom part of the pit.
The substrate for surface enhanced Raman scattering spectroscopy described in nonpatent literature 2 has gold covered on a silica columnar layer in a cap like form. The SERS effect is produced by gold placed on each columnar layer being adjacent to each other.